This application claims the priority of Korean Patent Application No. 10-2004-0081113, filed on Oct. 11, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical disc decoder system and, more particularly, to a digital signal processing method and apparatus for reading and processing data from an optical disc such as a DVD.
2. Description of the Related Art
An optical disc player reproduces data recorded on an optical disc medium such as a compact disc (CD) or a digital versatile disc (DVD). Specifically, in the optical disc player, a pick-up unit irradiates a track of the optical disc with a laser beam and detects pits on the optical disc based on variation in a reflected beam. Digital data recorded on the optical disc medium is thus reproduced.
Demodulation speed of the optical disc player is currently stabilized at approximately 16×. In addition, readability, which is the capability to read data having errors caused by a scratch or a defect on the optical disc, has become an important factor in the optical disc player. Accordingly, readability of the optical disc player is improved through repeated correction of burst, random errors, and so on. It is well known that in order to improve readability, the performance of an automatic gain controller, an equalizer, a data slicer, and a phase locked loop require enhancement. However, readability can also be improved by developing the ability to correct a larger quantity of data than is defined by DVD specifications.
In a conventional repetitive correction method, errors present in read data are corrected a fixed number of times, such as once (according to the sequence: PI (inner-code parity) correction-PO (outer-code parity) correction) or twice (according to the sequence: PI correction-PO correction-PI correction-PO correction). In this case, an error correction code (ECC) block operates to carry out error correction the predetermined fixed number of times, even when there are few or no errors. This occupies memory bandwidth and negatively impacts system throughput. Furthermore, error correction cannot be performed on input data having a multitude of random errors because the error correction sequence is carried out the fixed number of times.
Moreover, as the speed of optical disc systems continues to increase, repetitive error correction of more than two repetitions within one block cycle cannot be performed without increasing the operating frequency above 130 MHz when a cache is not used.
Meanwhile, erasure information for erasure-correcting a PI code, which is an inner code read from an optical disc, is generated by an eight-to-fourteen modulation EFM (or EFM+) demodulator of the optical disc player. Conventionally, when EFM and ECC blocks are de-coupled, a 1-bit erasure flag is added to each byte to generate 9-bit data. However, the 9-bit data is difficult to use when an SDRAM is used. Even when an internal SRAM or FIFO is used, it is difficult to generate the erasure information because the number of bits per word of the FIFO should be 9 bits in a repetitive correction mode, or because of a flag information timing problem.